1. Field of the Invention
The present invention relates to an improvement in the method of removing contaminating impurities from used battery acid fluid through extraction and filtration so to permit the fluid to be used in new batteries or concentrated for sale. In particular, the method employs a reduction process to regenerate strip acid employed in rejuvenating iron removing extractant.
2. Description of the Prior Art
In copending patent application Ser. No. 312,429, a method is disclosed of handling the serious economic and environmental problem of disposing of contaminated sulfuric acid (H.sub.2 SO.sub.4) solution contained in discarded lead-acid batteries. In order to reuse such solution in new batteries, it is necessary to remove various contaminating elements, the most serious of which being iron.
As disclosed in U.S. patent application Ser. No. 312,429, sulfuric acid from used lead-acid batteries may be reclaimed by employing discrete steps of filtration and extraction using an iron extractant agent comprising a mixture of a chelating agent, such as a derivative of an 8-hydroxyquinoline, an organophosphoric acid, a modifier, and a hydrocarbon carrier solution. Using multiple extraction steps, the extraction agent is mixed with contaminated battery acid fluid (diluted with distilled water or dilute sulfuric acid water) to remove the iron impurities. The extracted battery acid fluid is then filtered through a carbon filter to remove residual organics. The iron impurities are subsequently removed from the extraction agent in a concentrated form using a strip acid--permitting the extraction agent to be reused indefinitely. Through concentration or the addition of fresh sulfuric acid to overcome the water dilution, the reclaimed battery acid fluid may be placed in new lead-acid batteries. Tests reveal that this process produces a battery acid fluid which performs as well as fresh battery acid fluid, but is free of the costs and environmental risks of disposing of used battery acid fluid.
Although the above process functions exceptionally well, a new problem which emerges in reclaiming battery acid in this manner is that the strip acid becomes a by-product waste from this process which also must be disposed of. One method of increasing the efficient use of the strip acid is to use a counter-current rejuvenation process--whereby used strip acid having some iron content is contacted with extractant heavily contaminated with iron, and fresh strip acid is employed to remove the remaining contaminating iron from the extractant to complete rejuvenation. In this manner the iron content of the strip acid can be substantially increased before disposal. However, it is believed that the overall efficiency of the entire reclamation process may be even further improved if the iron content in the strip acid can be maximized.
Accordingly, it is a primary object of the present invention to increase the efficiency of battery acid reclamation by maximizing the amount of iron which can be removed from extractant through strip acid treatment.
Another object of the present invention is to provide an entire method of battery acid fluid reclamation which is commercially practical, requires minimal capital investment, is relatively inexpensive to operate, and minimizes environmental risk.